nodemap: introduce an option to use mmap to read the nodemap mapping
The performance and memory benefit is much greater if we don't have to copy all
the data in memory for each information. So we introduce an option (on by
default) to read the data using mmap.
This changeset is the last one definition the API for index support nodemap
data. (they have to be able to use the mmaping).
Below are some benchmark comparing the best we currently have in 5.3 with the
final step of this series (using the persistent nodemap implementation in
Rust). The benchmark run `hg perfindex` with various revset and the following
variants:
Before:
* do not use the persistent nodemap
* use the CPython implementation of the index for nodemap
* use mmapping of the changelog index
After:
* use the MixedIndex Rust code, with the NodeTree object for nodemap access
(still in review)
* use the persistent nodemap data from disk
* access the persistent nodemap data through mmap
* use mmapping of the changelog index
The persistent nodemap greatly speed up most operation on very large
repositories. Some of the previously very fast lookup end up a bit slower because
the persistent nodemap has to be setup. However the absolute slowdown is very
small and won't matters in the big picture.
Here are some numbers (in seconds) for the reference copy of mozilla-try:
Revset Before After abs-change speedup
-10000: 0.004622 0.005532 0.000910 × 0.83
-10: 0.000050 0.000132 0.000082 × 0.37
tip 0.000052 0.000085 0.000033 × 0.61
0 + (-10000:) 0.028222 0.005337 -0.022885 × 5.29
0 0.023521 0.000084 -0.023437 × 280.01
(-10000:) + 0 0.235539 0.005308 -0.230231 × 44.37
(-10:) + :9 0.232883 0.000180 -0.232703 ×1293.79
(-10000:) + (:99) 0.238735 0.005358 -0.233377 × 44.55
:99 + (-10000:) 0.317942 0.005593 -0.312349 × 56.84
:9 + (-10:) 0.313372 0.000179 -0.313193 ×1750.68
:9 0.316450 0.000143 -0.316307 ×2212.93
On smaller repositories, the cost of nodemap related operation is not as big, so
the win is much more modest. Yet it helps shaving a handful of millisecond here
and there.
Here are some numbers (in seconds) for the reference copy of mercurial:
Revset Before After abs-change speedup
-10: 0.000065 0.000097 0.000032 × 0.67
tip 0.000063 0.000078 0.000015 × 0.80
0 0.000561 0.000079 -0.000482 × 7.10
-10000: 0.004609 0.003648 -0.000961 × 1.26
0 + (-10000:) 0.005023 0.003715 -0.001307 × 1.35
(-10:) + :9 0.002187 0.000108 -0.002079 ×20.25
(-10000:) + 0 0.006252 0.003716 -0.002536 × 1.68
(-10000:) + (:99) 0.006367 0.003707 -0.002660 × 1.71
:9 + (-10:) 0.003846 0.000110 -0.003736 ×34.96
:9 0.003854 0.000099 -0.003755 ×38.92
:99 + (-10000:) 0.007644 0.003778 -0.003866 × 2.02
Differential Revision: https://phab.mercurial-scm.org/D7894
# A B
#
# 3 4 3
# |\/| |\
# |/\| | \
# 1 2 1 2
# \ / \ /
# 0 0
#
# if the result of the merge of 1 and 2
# is the same in 3 and 4, no new manifest
# will be created and the manifest group
# will be empty during the pull
#
# (plus we test a failure where outgoing
# wrongly reported the number of csets)
$ hg init a
$ cd a
$ touch init
$ hg ci -A -m 0
adding init
$ touch x y
$ hg ci -A -m 1
adding x
adding y
$ hg update 0
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ touch x y
$ hg ci -A -m 2
adding x
adding y
created new head
$ hg merge 1
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -A -m m1
$ hg update -C 1
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg merge 2
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -A -m m2
created new head
$ cd ..
$ hg clone -r 3 a b
adding changesets
adding manifests
adding file changes
added 4 changesets with 3 changes to 3 files
new changesets 5fcb73622933:d15a0c284984
updating to branch default
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg clone -r 4 a c
adding changesets
adding manifests
adding file changes
added 4 changesets with 3 changes to 3 files
new changesets 5fcb73622933:1ec3c74fc0e0
updating to branch default
3 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg -R a outgoing b
comparing with b
searching for changes
changeset: 4:1ec3c74fc0e0
tag: tip
parent: 1:79f9e10cd04e
parent: 2:8e1bb01c1a24
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m2
$ hg -R a outgoing c
comparing with c
searching for changes
changeset: 3:d15a0c284984
parent: 2:8e1bb01c1a24
parent: 1:79f9e10cd04e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m1
$ hg -R b outgoing c
comparing with c
searching for changes
changeset: 3:d15a0c284984
tag: tip
parent: 2:8e1bb01c1a24
parent: 1:79f9e10cd04e
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m1
$ hg -R c outgoing b
comparing with b
searching for changes
changeset: 3:1ec3c74fc0e0
tag: tip
parent: 1:79f9e10cd04e
parent: 2:8e1bb01c1a24
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: m2
$ hg -R b pull a
pulling from a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
new changesets 1ec3c74fc0e0
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg -R c pull a
pulling from a
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
new changesets d15a0c284984
(run 'hg heads' to see heads, 'hg merge' to merge)